1. Field of the Invention
The present invention relates to a solder recovering method and a solder recovering apparatus for separating and recovering a solder alloy and electronic components from a printed circuit board having the electronic components soldered thereon.
2. Description of Related Art
Printed circuit boards having electronic components mounted thereon are incorporated in home electric appliances such as video decks and television sets, or in electronic intelligence instruments such as microcomputers and facsimile machines. These electronic components are mounted on the printed circuit board by bonding with solder. When the home electric appliances or electronic intelligence instruments have gone out of use due to breakdown or superannuation, they are scrapped.
The scrapped home electric appliances and electronic intelligence instruments are collected as incombustible refuses and are usually, without being incinerated, treated as landfills as they are or as shredder dusts after being shredded into pieces. Consequently, once the home electric appliances or electronic intelligence instruments are treated as landfill refuses, the printed circuit boards packaged therein are also brought into landfills.
The solder used for mounting of the electronic components is an alloy of lead and tin. Although lead is stable without dissolving in water near the neutral pH, it has a property of dissolving in acidic water. Therefore, when exposed to acidic rain, lead in the solder alloy on the printed circuit board dissolves, arising a possibility of polluting soil and groundwater. If a person ingests groundwater polluted with lead, the groundwater may cause various health disorders ascribed to lead. However, there are currently no appropriate measures for preventing lead contained in the solder of the scrapped printed circuit board from dissolving out.
In addition, the scrapping by landfill of the home electric appliances or electronic intelligence instruments causes metallic resources to be wasted, because the solder alloys in the printed circuit boards mounted on the home electric appliances or electronic intelligence instruments are never used again.
A method for recovering solder from a printed circuit board is disclosed in Japanese Laid-Open Patent Application No. Hei 7-336042, in which a liquid heat medium, such as an oil kept at a high temperature, is sprayed onto the printed circuit board to melt the solder, and the melted solder is wiped off to recover the solder.
However, in the method described above, since only a liquid such as an oil is sprayed, the mass of the fluid is relatively so small that the solder and electronic components are removed from the printed circuit board with poor efficiency. Besides, since a means for transporting the fluid must be a mechanical one, the construction for recovering solder becomes complicated.
It is an object of the present invention to solve the foregoing problems and to provide a solder recovering method and a solder recovering apparatus for efficiently separating and recovering a solder alloy and electronic components from a printed circuit board.
It is another object of the present invention to provide a solder recovering method and a solder recovering apparatus for separating and recovering a solder alloy and electronic components from a printed circuit board by spraying, onto the printed circuit board having the electronic components soldered thereon, a mixed fluid composed of a liquid heat medium and metal particles and kept at a temperature above the melting point of the solder alloy.
It is a further object of the present invention to provide a solder recovering method and a solder recovering apparatus for easily separating and recovering a solder alloy and electronic components by adjusting the specific gravity of each of the solder alloy, metal particles, liquid heat medium and electronic components.
These and further objects, features and advantages of the present invention will become apparent from the following detailed description of a preferred embodiment thereof taken in conjunction with the accompanying drawing.